This invention relates to drag reducing means on waterborne vehicles and more specifically to the use of high molecular weight water soluble polymers with drag reducing properties in a water ablative paint coating.
The relative flow of water past the surface of a waterborne vehicle of either the submerged or surface type creates various drag forces which resist the forward movement of the vehicle. One form of drag known as shear is due to the fact that water is slightly viscous and a boundary layer exists immediately adjacent to the submerged surface of the waterborne vehicle. The shearing of the viscous fluid, or water, in this region causes drag. Another contribution to drag results from turbulent flow. At the bow of the vehicle the flow of the liquid along the frontal contour is laminar and fairly uniform, with no apparent evidence of roiliness. This flow continues to a point on the vehicle surface at which smooth flow is interrupted and turbulence become manifest. This results in skin friction or drag. Proceeding to the tail where a fluid pressure rise occurs the boundary layer often separates from the object creating a void or cavity in the fluid. This results in a situation where the object cannot benefit or recover a thrust from the pressure rise at the stern. This suction-like effect is referred to as pressure drag. In summary, all of these drag forces can be considered as reverse forces which contribute to a decrease in speed of an object traversing through water.
Various studies have shown that polyethylene oxide and certain polyacrylamide resins possess properties that minimize drag or skin friction and various proposals have been made in order to provide a means whereby enrichment of the boundary layer with these drag reducing polymers can be effected. These have included the injection of concentrated solutions into the boundary layer and by coating the object with drag reducing polymers. The coating techniques cover sheet production by extrusion and calendering powder spraying at elevated temperatures, and isostatic pressing. Insofar as is known, no proposal has included paint coatings.